Keywords: Perfusion, Perfusion

Motivation: DSC is the leading methodology for MR-based perfusion imaging. However, the technique's reliance on invasive gadolinium injections poses a major limitation.

Goal(s): Can breath-holding induce perfusion contrast that is exploitable using DSC MRI?

Approach: Ten healthy subjects underwent MRI at both 3T and 7T, while performing eight 16 s breath-holds. Breath-hold-induced signal changes were fed into a DSC MRI analysis pipeline, and perfusion was quantified.

Results: Calculated cerebral perfusion values were within the physiological range of literature values; the breath-hold task yielded significantly higher contrast-to-noise and GM-to-WM contrast with higher field strength and increased scan time, although this plateaued at roughly 6 min.

Impact: For the first time, we show that DSC-MRI using breath-holding allows for the quantification of perfusion parameters. This may have broad implications for neurovascular disease, either circumventing the need for invasive gadolinium injections or shedding additional light into pathology.

Keywords: Arterial Spin Labelling, Pulse Sequence Design

Motivation: Comprehensively characterizing cerebrovascular events including dynamic blood flow patterns and downstream perfusion is important in clinical diagnosis of cerebrovascular disorders.

Goal(s): To develop a time-efficient phase-sensitive ASL technique (PS-ASL) that provides high-quality time-resolved 4D-MRA and perfusion imaging within single scan.

Approach: PS-ASL sequence was designed by combining pCASL and PASL preparations with stack-of-stars golden-angle radial acquisition and a self-constraint low-rank subspace reconstruction. The label and control pulse modules alternated between pCASL and PASL preparations in each TR. Phase-sensitive subtraction between control and label yields 4D-MRA from PASL and perfusion from pCASL.

Results: Both dynamic 4D-MRA and perfusion maps were successfully obtained by PS-ASL.

Impact: The developed PS-ASL technique could be a potential powerful imaging tool in clinical applications, which provides detailed characterization of blood flow from both arterial and capillary beds in a single sequence.

Keywords: Neurofluids, Neurofluids

Motivation: The difference in mLVs outflow between healthy control (HC) and brain disorder patients may contribute to toxic protein aggregation and cognitive decline.

Goal(s): To demonstrate mLVs structure and flow information of brain disorder patients and compare quantitative flow metrics between HC and patient

Approach: We applied IR-ALADDIN to acquire mLVs images around superior sagittal sinus in 20 HCs and 9 patients with various brain disorders such as meningioma, hydrocephalus.  

Results: The mLVs size was reduced in patients compared to HC with no significant difference in mLVs velocity, leading to overall mLVs flow reduction in patients.

Impact: The reduced mLVs flow in brain disorder patients was confirmed using a non-invasive technique. This suggests the possibility to study relationship between brain disorders and waste clearance through the mLVs flow in further studies.

Keywords: Contrast Agents, Perfusion, brain

Motivation: Provide direct measurements of cerebral perfusion metrics, relative cerebral blood flow and volume, and mean transit time.

Goal(s):  Generate a known step susceptibility contrast input rather than requiring back calculation of an arterial input function 

Approach: We used a step reoxygenation of previously deoxygenated lung alveoli to induce a step increase in oxyhemoglobin in arterial blood and analyzed the T2*-weighted signal for each voxel. Perfusion metrics from step deoxyhemoglobin changes were compared to those from conventional analysis using a gadolinium contrast agent in healthy volunteers.  

Results: The perfusion metrics from the step deoxyhemoglobin method were similar to those from Gadolinium injection.  

Impact: Perfusion metrics can be measured directly from a non-invasive test using a step decrease in deoxyhemoglobin generated by instantaneous reoxygenation from a brief hypoxia. They correspond to those calculated indirectly from an intravenously injected Gadolinium contrast agent involving complex analysis.  

Keywords: Arterial Spin Labelling, Vessels

Motivation: T2-relaxation-under-spin-tagging(TRUST) is a non-invasive MRI technique to estimate blood oxygenation in the superior sagittal sinus from a T2 decay fit.

Goal(s):  The calibration curve to convert T2 into oxygenation has been derived with ex-vivo experiments for healthy volunteers and patients with specific types of sickle cell disease.  

Approach: Validation of these calibration curves is difficult because blood cannot be drawn from the superior sagittal sinus itself, hampering implementation of the technique in other patient groups. 
 

Results: Here, TRUST was adapted and optimized for the arm so that its measurements of venous oxygenation can be directly compared with venipunctures from the cephalic vein.

Impact: The TRUST-sequence was optimized for non-invasive T2-measurement in the upper arm veins. A posteriori correlation with blood properties returns a venous oxygenation mapping. This may confirm the currently used calibration curve and facilitate obtaining accurate calibration curves for specific diseases.

Keywords: Hybrid Imaging, Molecular Imaging, Optoacoustic (Photoacoustic) Imaging

Motivation: Interpreting BOLD signals in fMRI studies is a challenging task due to their dependence on multiple factors.

Goal(s): Multiparametric readouts from a recently developed hybrid magnetic resonance optoacoustic tomography system can offer unprecedented capabilities for studying the rodent brain in resting-state conditions.

Approach: Simultaneously acquired multimodal functional data of mice were utilized to link hemoglobin resolved optoacoustic readouts to BOLD.

Results: Multiparametric brain-wide activity were detected under resting-state condition for the first time. Revealed functional connectivity maps and brain networks showed high spatial overlap among the hemodynamic components. BOLD and total hemoglobin functional connectivity were found tightly correlated, compared to oxygenated- and deoxygenated-hemoglobin.

Impact: Hybridization of optoacoustic tomography and MRI is a powerful multi-modal approach due to highly complementary contrasts and capabilities for functional neuroimaging. The more comprehensive functional readings provide unique capabilities for studying neurovascular and neurometabolic coupling mechanisms and related diseases.

Keywords: Arterial Spin Labelling, Arterial spin labelling

Motivation: Cerebral blood flow (CBF) is a fundamental physiological measure indicating regional brain function and vascular conditions via arterial spin labeling (ASL) perfusion MRI, but ASL sequences is limited.

Goal(s): Blood-oxygen-level-dependent (BOLD) fMRI is known to be a function of CBF and other physiological sources. We try to extract CBF information from BOLD signal.

Approach: We proposed a convolutional neural network to extract CBF from BOLD fMRI signal.

Results: We confirmed the possibility of using supervised deep learning model to extract CBF from BOLD fMRI from independent sequences.

Impact: Deep learning enables the estimation of CBF signal directly from the prevalent BOLD fMRI images, offering an alternative to the ASL sequence that is not universally available across research facilities.

Keywords: Arterial Spin Labelling, Arterial spin labelling, Challenge; multi-PLD ASL

Motivation: The OSIPI ASL Challenge is a community initiative motivated by open science principles that aim to establish good practices in ASL image analysis and Cerebral Blood Flow (CBF) quantification.

Goal(s): The second ASL challenge's main goal is to provide a thorough comparison of existing post-processing pipelines focusing on Multi-PLD methodology.

Approach: The second roadmap will provide different datasets; a population dataset which will bring real variability to the challenge and synthetic data which allows straightforward ground truth comparison.

Results: The second edition of the ASL Challenge will contribute to gaining new insights into the potential sources of variability within the multi-PLD analysis pipeline.

Impact: Through the second edition of the ASL Challenge, we seek to enhance our understanding of multi-PLD analysis in the ASL community. Its success could establish a consensus on the processing of multi-PLD ASL data, positively influencing clinical and scientific practices.

Keywords: Perfusion, Quantitative Imaging, CBF, perfusion, quantification, flow-related enhancement, pCASL, imaging speed optimization

Motivation: Flow-related enhancement (FREE)-MRI could be used to generate phase-resolved perfusion-weighted brain maps.

Goal(s): To test cerebral blood flow (CBF) estimation using the pulse wave amplitude in FREE-MRI. Secondly, the potential for acceleration was evaluated retrospectively.

Approach: Twenty-four healthy subjects had cerebral MRI with balanced steady-state free precession imaging (FREE-MRI) and with pCASL-MRI for comparison.

Results: The value distribution of the estimated CBF showed disparity of the values between both techniques in the histogram. A Kolmogorov-Smirnov test confirmed differing probability distributions.
The approximated CBF from FREE-MRI remained stable until 50% of the data was reconstructed and reveals large potential acceleration. 

Impact: The proposed technique allows a rough approximation of the cerebral blood flow. Further sequence optimization must be achieved to improve the measurement of lowly perfused tissues. Nevertheless, the technique offers large potential for imaging speed optimization.

Keywords: Velocity/Flow, Velocity & Flow

Motivation:  4D flow imaging in the liver suffers from long acquisition time and inefficient motion control.

Goal(s): Address the challenges of prolonged acquisition time and significant motion artifacts in hepatic 4D flow imaging.

Approach: We collected data from all respiratory states without a diaphragm navigator, and retrospectively reconstructed respiratory-resolved 5D flow using simultaneously recorded breathing signal.

Results: This scheme reduced the acquisition time from over 10 minutes to 6-8 minutes, while maintaining consistent image quality with few motion artifacts. High quantitative correlation in hepatic hemodynamic results was found between the results from prospectively navigated data and retrospectively binned data.

Impact: The proposed hepatic 5D flow scheme achieved high image quality and quantitative metrics, compared with those of diaphragm navigated results. This scheme can effectively shorten the acquisition time to 6-8 minutes and mitigate motion artifacts.

Keywords: Contrast Agents, Blood vessels, Time of flight magnetic resonance venography, Iliac vein compression syndrome

Motivation: The use of respiratory-gated TOF-MRV in assessing the degree of iliac vein compression is easily affected by respiratory uniformity, leading to vascular distortion and corresponding false images.

Goal(s): This study evaluated the diagnostic effectiveness of an improved TOF-MRV (mTOF-MRV) in  Iliac vein compression syndrome (IVCS) diagnosis by optimizing key parameters, compared with conventional TOF-MRV.

Approach: Objectively evaluated the deviation of vascular stenosis degree between TOF MRV and mTOF MRV using DSA as the standard.

Results: The mTOF-MRV has better image quality and can accurately detect venous stenosis. It can be applied in the diagnosis of IVCS and further assessments after endovascular interventions.

Impact: mTOF-MRV more accurately located iliac vein stenosis without obvious stair-step artifacts and magnetic sensitivity artifacts, thereby meeting the diagnostic and clinical requirements It can be applied in the diagnosis of iliac vein compression syndrome and further assessments after endovascular interventions.

Keywords: Multi-Contrast, Brain, Myelin plasticity, diffusion MRI, DTI, corticospinal tract, hippocampus, cerebellum, sensory motor system

Motivation:  MRI studies have demonstrated plastic changes in grey and white matter (GM/WM) during motor skill learning. However, diffusion magnetic resonance imaging (dMRI) might provide additional complementary information in contrast to multi-parametric mapping (MPM), which has been investigated previously. 

Goal(s): To investigate training-induced neuroplasticity using dMRI and contextualize them to the MPM findings.

Approach: Acquisition of longitudinal dMRI and MPM during motor skill learning.

Results: We observed overlapping changes in dMRI and MPM metrics following motor skill learning. dMRI was thereby able to capture additional changes within the WM, whereas within the GM, some findings were unique to the MPM protocol.

Impact: dMRI and MPM metrics are sensitive to motor skill learning-induced changes in GM and WM. To combine the two methodologies advances our capability in detecting neuroplasticity changes and might be beneficial for patient rehabilitation.

Keywords: Perfusion, DSC & DCE Perfusion, Head & Neck Imaging

Motivation: To use fluid-mechanics based deep learning method to predict perfusion parameters from dynamic images

Goal(s): We propose to explore the possibility to use neural network trained on simulated data from fluid mechanics simulation to analyze dynamic medical images.

Approach: We use quantitative transport mapping network (QTMnet), which is trained on simulated concentration propagation profile generated from constrained constructive optimization (CCO)  and transport equation-based tracer propagation simulation, to predict perfusion parameters including flow rate, permeability, vasculature volume, from DCE MRI images.

Results: QTMnet predict perfusion parameters accurately in simulation study and can distinguish different gene expression group patients comparing with using traditional kinetics model.

Impact: Proposed QTMnet method can be used to predict different perfusion parameters related to dynamic images accurately and automatically without usage of arterial input function.

Keywords: Arterial Spin Labelling, Arterial spin labelling, Perfusion, Myocardium, T1 Mapping, T2 Mapping, Reproducibility

Motivation: Contrast-agent free techniques are needed in cardiac MRI studies for assessment of patients with coronary artery disease but with contraindications to gadolinium contrast-agents, such as kidney disease.

Goal(s): The aim of this work was to assess the intra and intersession reproducibility of a multiparametric protocol including three non-contrast techniques (ASL, native T1 and T2 mapping) in healthy controls with a wide age range to eventually test the technique in clinical patients.

Approach: Multiparametric non-contrast cardiac MRI in ten healthy controls at 1.5T.

Results: This protocol can offer contrast free alternative for perfusion quantification, T1 and T2 mapping, with good intra and intersession reproducibility.

Impact: Multiparametric cardiac MRI with arterial spin labelling (ASL) perfusion, T1 and T2 mapping could offer a contrast-agent free alternative for patients with kidney disease, or other contraindication to gadolinium agents, with good intra and intersession reproducibility.

Keywords: Arterial Spin Labelling, COVID-19

Motivation: A proportion of patients admitted to hospital with SARS-CoV-2 infection have cognitive deficits that persist for several months. However, the mechanisms behind persistent neurological symptoms are unclear. Blood-brain barrier (BBB) dysfunction is a possible underlying cause.

Goal(s): We aimed to investigate BBB permeability in participants previously admitted to hospital with SARS-CoV-2 infection (post-acute COVID-19).

Approach: We used a diffusion-prepared pseudo-continuous arterial spin labelling (DP-pCASL) to quantify water exchange rate in post-acute COVID-19 participants and controls.

Results: Post-acute COVID-19 participants demonstrated lower whole brain water exchange rates across the BBB than controls, but no differences in arterial transit time or cerebral blood flow.

Impact: This is the first study to report reduced water exchange across the blood brain barrier in the context of post-acute infection with SARS-CoV-2. This may implicate glymphatic system dysfunction as a mechanism for neurological symptoms associated with long COVID-19.

Keywords: Arterial Spin Labelling, Arterial spin labelling, Simulation

Motivation: We identified a gap in understanding multi-tag Time-SLIP MRI dynamics, crucial for advanced perfusion analysis, particularly in varying physiological and pathological states.

Goal(s): Our goal was to develop a comprehensive simulation tool to accurately predict signal changes in multi-tag Time-SLIP ASL MRI across diverse flow conditions.

Approach: We employed MATLAB to simulate numerically non-selective and  selective multi-tag Time-SLIP pulse sequences, applying Bloch equations to model tissue-specific magnetization and blood flow perfusion dynamics.

Results: Simulations showed distinct magnetization patterns between odd and even pulse tags, aligning with physiological flow rates.

Impact: This simulation tool enables researchers to customize Time-SLIP MRI protocols for detailed study of fluid dynamics across the body, from blood to CSF flow. It provides a solid foundation for developing more comprehensive ASL-related simulations.

Keywords: Arterial Spin Labelling, Perfusion, Pediatrics

Motivation: Moyamoya is a progressive cerebrovascular disorder affecting hemodynamics and the disease often begins during childhood. However, the non-invasive assessments of hemodynamics in pediatric Moyamoya patients remain an open question.

Goal(s): Investigate the CBF change before and after revascularization in pediatric Moyamoya patients.

Approach: CBF in 42 patients was measured using arterial spin labeling on a 3T MRI 1 week before and within 2 weeks after revascularization. CBF in regions affected by vasculopathy was compared before and after revascularization.

Results: CBF in regions affected by vasculopathy increased significantly after revascularization.

Impact: ASL can be utilized to evaluate CBF in pediatric Moyamoya patients before and after direct revascularization.

Keywords: Perfusion, Contrast Mechanisms, breast tumor; Ultrafast Breast MRI

Motivation: Ultrafast (UF)-DCE MRI is a novel approach to obtain kinetic information very early after enhancement, which promises improved capabilities in differentiating malignant from benign lesions of breast cancers.

Goal(s): The early hemodynamic characteristics of lesions using breast UF-DCE MRI were systematically investigated to evaluate the value of the relevant kinetic parameters in the diagnosis of different grades of breast cancer.

Approach: The kinetic parameters of UF-DCE MRI were calculated to differentiate the different grades of breast cancer. 

Results: The kinetic parameters of UF-DCE MRI can be used to distinguish high-grade from benign and low-grade breast cancer.

Impact: Breast ultrafast DCE MRI was used to explore the early hemodynamic characteristics of the lesions and evaluate the value of the relevant dynamic parameters in the diagnosis of different grades of breast cancer.

Keywords: Velocity/Flow, Brain, Cerebrovascular health & arterial stiffness

Motivation: Arterial stiffness, a key marker of cardiovascular health, can be monitored by measuring pulse-wave velocity. However, current methods do not extend into the brain due to an inability to resolve the pulse waveform on a beat-to-beat basis for intracranial arteries.

Goal(s): Our goal is to demonstrate the concept of measuring intracranial pulse-wave velocity using dynamic inflow magnitude contrast (DIMAC) MRI.

Approach: We measured intracranial pulse-wave velocity by measuring the pulse-wave delay between internal carotid and middle cerebral arteries.

Results: The arterial pulse-wave delay between the internal carotid artery and the middle cerebral artery was 29±14ms, corresponding to a pulse-wave velocity of 6.8±2.2m/s.

Impact: These results are the first stage in establishing pulse-wave velocity as a new non-invasive MRI biomarker for cerebrovascular health, providing a novel tool to investigate the role of arterial stiffness in healthy ageing and brain pathology.

Keywords: Perfusion, Velocity & Flow, Cerebrovascular reactivity

Motivation: Caffeine, one of the widely used psychoactive substances is known to reduce basal cerebral blood flow (CBF). However, its effect on vasodilatory capacity has not been characterized

Goal(s): To evaluate the impact of Caffein on cerebrovascular reactivity (CVR)

Approach: 8 healthy caffeine-naïve volunteers were scanned for baseline (pre-caffeine) and post-Caffeine CVR measurements using BOLD MRI and phase-contrast MRI (PC)-MRI during normal air breathing and hypercapnia using 5% CO2 enriched gas mixture

Results: There was a significant reduction in blood-flux (BF) during room-air (p=0.002) and hypercapnia (p=0.0015) post caffeine administration (variation=33.7% and 41.3% respectively). PC-CVR and BOLD-CVR were reduced by 32.7%(p=0.006) and 22.5%(p=0.006) respectively

Impact: This study's findings provide valuable insights into the impact of caffeine on cerebrovascular reactivity (CVR), revealing a significant reduction after caffeine intake. Findings would be beneficial in reducing the inter-subject variability of CVR by improving the sensitivity in detecting abnormalities.